This study will help us decide the best way to image the knee for diagnostic purposes: Knee computed tomography vs knee x-ray. The computed tomography will provide a weight bearing 3D view.

This will be an ancillary study to the Multicenter Osteoarthritis Study (MOST) second renewal #201511711). Using a prototype Curve Beam Standing Computed Tomography (SCT) scanner to get a 3 dimensional picture of the knee joint, bilaterally. This scanner by Curve Beam 175 Titus Ave, Suite 300, Warrington, Pennsylvania 18976, has been approved by the Food and Drug Administration (FDA) for ankles and feet. This has been modified to do the scan of the knee but is not yet approved by the FDA for the knees. The proposed ancillary study would add the key benefit of providing more sensitive and accurate identification of prevalent knee osteoarthritis (OA) at baseline and incident knee OA at follow-up than is available with plain radiographs. In addition, it would enable biomechanical modeling of the knee joint on a larger scale than achieved in any prior study, allowing testing of biomechanical hypotheses regarding mechanisms of disease development and progression that have not been possible on this scale previously.

Inclusion Criteria:

Only participants in the Multicenter Osteoarthritis Study (MOST) who attend a 0/144-month visit at the Iowa site are eligible for inclusion.

Additional Inclusion Criteria Include:

• Completed knee radiograph (posteroanterior view) at 0/144-month visit of primary MOST-second renewal study at the Iowa Site

Exclusion Criteria:

• Bilateral Total Knee Arthroplasty

The existing cohort will be age 62-92 years, average age approximately 71 years, at the start of this study. This cohort will consist of participants who already have symptomatic knee OA, in many cases advanced disease, or who had risk factors at the start of MOST but have not developed symptomatic knee OA. All of the existing cohort who have 1 or 2 "native" knees will be approached providing native knees are not considered to be KL grade 4 (bone on bone). The new cohort will consist of subjects with knee pain, aching or stiffness at baseline and participants without any knee symptoms in the previous 30 days. Both knees with KL grades of radiographic OA of 0, 1, or 2 in the tibiofemoral (TF) and patellofemoral (PF) compartments.

As an ancillary study to the Multicenter Osteoarthritis Study (MOST), data will be available to other researchers through the MOST Data Sharing Plan.

Following study completion (anticipated August 2021)